Electric furnace



y 1929; F. A. J. .FI TZ QERALD 1, 14,081

ELECTRIC FURNACE Original Filed May 26, 1925 2 Sheets-Sheet l' s N l. E i amnim +Fmmz3AJIlZ556raZd Patented May '21, 1929.

UNITED STATES 1,714,081 PATENT OFFICE.

FRANCISA. J. FITZ GERALD, OF NIAGARA FALLS, NEW YORK, ASSIG-NOR TO HARPER ELECTRIC FURNACE CORPORATION, A CORPORATION OF NEW YORK;

ELECTRIC FURNACE.

Original application filed May '26, 1925, Serial No. 32,879. Divided and this application filedlay 13,

1927i Serial No, 191,046.

This invention relates to electric furnaces of the resistance type which may be used for heat treatingsubstances and bodies of different kinds and forms ina variety "of ways,

such as curin ,baking and glazing ceramic bodies; annea ing, tempering, welding and fusing metal"; and cremating, .firin'gland burning materials and bodies.

Among theohjects of my invention is-to provide an improved electric furnace which shall be simple and economical in construction, durable in use, and which may be easily and efliciently operated.

In the preferred embodiment of my invention, I provide an electrically heated furnace wherein the resistors are contained within a closed heat chamber that may bekept filled with a gas, vapor or fume of such kind or quality as will render the resistorsimmune to, or protected from, deterioration such as may be caused by oxygen of the air or gases v arising from the material being treated. The

material or articles to be'treated are contained in a chamber adjacent to the heat chamber but separated therefrom by .a septum formed of material which is highly receptive, conductive and emissive of heat but is substantially non-reactive inthe presence of atmospheric oxygen at high temperatures; he material forming the septum or' division between the heat chamber and the chamber containing the material treated forms one of the important features of my invention. I preferably form the septum of silicon carbide such as carborundum, and particularly a form of silicon carbide which I will describe indetail hereafter. In. the preferred form of my invention, I also line the walls of the heat chamber with this material so as to provide a path along which radiant heat received by the'walls of theheat chamber may be conducted to the chamber containing the material treated.

'Nume'rous objects and advantages of my invention will appear from the following description, taken in connection with the accompanying drawing, wherein Fig. 1 is a view, partly in section on the line A of Fig. 2, partly in elevation and partly broken away, of a furnace disclosing one embodiment of my invention.

Fig. 2 is a section, partly broken away,

- taken on the line'B of Fig. 1.

Fig. 3 is a transverse section on a somewhat enlarged scale taken on the line C of F1g.'1.and showing certain further details of construction.

.Fig. 4 is a diagrammatic view of a preferred arrangement and disposal of the furcommedcial commodity in regular sections up A to 4 x 10 in. of from 4 to 6 ft. in length. For certain purposes it is preferable to machine or saw the sides at an angle as shown at 7 in Fig. 3 so as to give a greater radiating surface to .the lower face 8 of the resistor 5. The resistor 5 is supported by means of carbon.- aceous terminals, '9, 10 as shown in Figs. 1, 2 and 3 projecting through the wall of the furnace. The connection between the, terminals and resistor may be formed by a slip joint. If desired to secure adequate electrical connection with the terminals, such joint may be formed to provide a wedge fit, or such connections completed by packing with powdered graphite or carbonaceous material, not

shown. In this manner, the resistor is supported between the terminal connections. When a resistor is desired of greater length than can readily be produced as a monolith, it is quite feasibleto join two or more' of such resistors together, end to end, as by capping their contiguous ends Within the fur-' nace; or, if desired, central terminal or terminals may be extended through the furnace walls and coupled together as shbwn in Fig.

4: outside of the furnace wall which is indicated by a dotted line 16 in'Fig. 4.. When arranged in this manner the two resistors may; be operated in series from a source of current 12, or if it isdesired to operate one of the rasistors at a higher temperature than theother overload, thereby avoidingthe loss of the charge.

The resistor chamber D is bounded by relatively massive roof-slabs, or tiles, 17,'

side-slabs 18, 19 and floor plates 20,- all being supported by another series of silicon carbide.

uprights 21 and-foot-blocks 22, leaving an interposed gap E connecting with an enlarged runway F, to receive a car, or series of cars, as 23, 24 and 25, mounted on wheels 26 and whose upper plates, or

. platforms, as 28 Figure 3, are also formed of silicon carbide. The said floor plates 20, constitute a heat-transferring septum from the resistor chamber D, to the underlyingcon- .duit chamber H. Paralleling the outersurfaces of the; chamber walls are Wall gaps filled with silicon carbide sand, 29. The outer roof may be suitably formedto receive pulverized, non-heat-conductive refractory ,ma-' terial and the entire furnace may then be further'enveloped with material most effective to .30 resist the outward flow of low-temperature heat, as indicated by the broken contour line It 'will now doubtless be apparent that the path of least resistance for the flowof heat units from the lower surface of the resistorwill be, as see arrows at, to andthence, by conduct-ion, through the septum, from whence they proceed, by radiation, as seearrows b to the car-platforms and whatever may be .n1'ounted thereon. Concurrently, how ver.

and particularly from its sides, resistor heat will be imparted, as see arrows of to the resistor chamber side walls, it being tjacnce most freely conducted downwardly into thev supporting side walls, and foot blocks, escap- 1 ing by radiation, as see arrows d, to the-charge and the car platform.- Naturally, a portion of the transferred energy is lost through the car-clearance spaces of the gap E; but the actual sum of this,.relative to the whole, is comparatively nominal and usually negligible.

, As the mass of downwardly heat-conducting silicon carbide in the Walls of.the rethan that of the resistor, and as these silicon carbide walls conduct the heat from the resister with a comparatively small drop in temperature, and as this greater mass of 'sllicen carbide serves as a heat reservoir, therefore fluctuations of temperature directly in and at the resistor itself are diminished.-

cases it is feasible to employ an enveloping sistor'chamber may be many times greatertemporary binder such as flourpaste or the like, and is then molded into the desired forms. The articles thus formed are then heated in an electric furnace to the temperature at which silicon'carbide is, formed, with the result that recrystallization occurs and a dense, monolithic mass is obtained. The blocks, slabs or tiles so'formed are then placed in'the furnace structure in position to form the linings of the chambers and the septum between the chambers and the furnace may then be heated in the usual manner so as to cause further recrystallization of the silicon carbide, thus causing adjacent blocks to coalesce, and the septum and chambers are automatically formed jdevoid of joints. I have indicated the union ofthe joints by coalescence by wavy lines 31 and 32 in Fig. 3. At the high temperature at which the furnace operates, oxygen must be excluded from the chambercontaining the resistor, or such chamber must contain a gaseous medium which will it'selfreact with and wholly con- 'vert any oxygenwhich might otherwise reach the resistor and its juncture with the terminals.- The inert gas may be introduced into the resistor chamber by means of a refractory tube 33, Fig.3, and held under a head or pressure above that of atmosphere. In certain atmosphere of -volat'ilized zinc, that is, zinc. gas or zinc fume, The supply of this material can readily be maintained by an occasional introduction into the chamber D of molten zinc. In addition to its functioning as an inert gas, zinc gas functions as an absorbing agent by being converted by any oxygen present to zinc oxide, which eventually fills all e r'evices and prevents escape oflthe metal. Due to this self sealingproperty, a nominal renewal only of the zinc is required to main tain a sufiicient quantityin the heat chamber, such renewal being merely such as to supply that lost by ventage-escape to avoid an excessive development of pressure within the chamber. A further advantage of the use of the zinc gas is that it forms an effective heatconvective agent. v

Lower tubes 34, Figures 1 and 3, leading to the-conduit chamber, may serve a dual purpose; to permit the escape, or the withdrawal by suction,- of air, gases and/or vapors; also .to introduce gases and/or vapors, as for the purpose of producing reducing at-- mospheres.

A plurality of cars, as 23, 24, 25 of Figure 1, each abutting upon another, may be continuously impelled through the furnace conduit at such a rate of motion that, to illus-. trate, when car 23 will have reached the position occupied by car 25, which is the hot zone of the conduit, the charge conveyed by that car will then be adequatelyheat-treated. If desired, as in thefusion of non-ferrous metals, annealing iron, or heating steel for battened tightly, as at Z,

. as in the case of ceramics, a dual furnace can, readily be constructed, each unit standing side by side, whereby the charge cars can readily be switched at the terminals, circulatingthrough the chamber conduits with but a nominal heat loss from the cars themselves. I

I find that the life of resistor or resistors, when operated according to the conditions above set forth, is practically interminable.- Nevertheless, should a fracture occur, as from accident or a very slow but progressive oxididation sufficient to eventually. cause it to ,sag and pull apart,it will beperceived,

by referenceto Figures 1 and 3, that the upper or-roof portion ofthe furnace can .readily be broken away, permitting a sub- .stitution of resistors even'when the internal chamber-temperature is quite. high.

- Temperatures in this furnace can be readily -lcontrolled, forindefinite time periods, withinv plus and minus tolerances of, say, 5 to 10 'C..; but this condition is largely dependent upon pyrometry,

In certain cases, various modifications of the structure and method of operation above described may be made. Thus, in certain cases a carbon or graphit-ized carbon resistor, even when of the zigzag form, will function satisfactorily if the space within its containing chamber is filled with silicon car- I hide, or with granular carbon or pulverized graphite. Again, the slab. formed of angular cross section of zigzag resistor need not necessarily be adhered to in that itmay be cylindrical in transverse section, being encased in a silicon carbide'tube or otherwise formed; It has been found that the graphite resistor can be greatly improved in its physical properties by undergoing heat treating process. This can be carried out by passing current of electricity through the resistor while it is protected from oxidation so as to heat it to a temperature at least as high or considerably higher than that at which it will be used in actual practice. When this is done it is foundthat the resistor is much tougher and more resilient than it was originally and consequently far less likelyto be broken by e be enclosed and a nal mechanical forces which would tend to break it.

This is a division of my co-pending application, Serial No. 32,87 9, filed May 26, 1925, I

for electric furnace.

I claimt 1. An electric furnace for heat treating substances having a resistor chamber containing an inert atmosphere,.a heat treating chamber containing a gas having a pyrochemical and physical action on the substances heat treated and a-septum between said chambers that will not deteriorate when heated to a high temperature and subjected to a reducing atmosphere within the resistor chamber and a gas having apyrochemical and physical action on the substances being heat treated within the heat treating cham-' her. a r

2. 'An electric furnace for heat treating substances having a resistor chamber formed with a recrystallized silicon carbide lining for said chamber containing a metallic gas, a heat treating chamber having means for introducing therein a gas having a pyrochemical and physical action on the substances heat treated and a recrystallized silicon carbide septum between said chambers.

3. An electric furnace for heat treating substances having a resistor chamber containing an inert gas under pressure above that of atmosphere, a heat treating chamber, means'connected to said'heat treating chamber for withdrawal or introduction of gases therein and a septum between said chambers- -preventing intermixture of the gases contained within said chambers but permitting heat transfusion from theresistor chamber to the heat treating chamber.

4. An electric furnace for heat treating substances, a resistor chamber, a zigzag car bon resistor enclosed within said chamber, means connected to said chamber for intro: ducing into said chamber containing an inert zinc gas under pressure above that of atmosphere as an absorbing agent, a portion of which is adapted to be converted by any oxygen present within said chamber to zinc oxide to form a seal for preventing escape of said gas. 1

FRANCIS FITZ GERALD.-

CERTIFICATE or CORRECTION.

Patent No. 1,714,081. Granted may 21, 1929,

, FRANCIS J. rm GERALD.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, lines 59 and 60, for the misspelled word."f urname" read "fumace"; line'67, for "commedcial" read "commercial";" and lines 97and' 98, for "resistors" read "resistors"; page 2, lines 63 and 64, strike out the word "carborundum"; tiage 3, line 97, claim 4, strike out the word "containing"; and that the said Letters Patent should be read with these, corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 30th day of July, A. D. 1929.

M. J; Moore,

. (s l) Acting Commissioner of Patents.

CERTIFICATE OF CORRECTION.

Patent No. 1,714,081. Granted May 21, 1929, to

FRANCIS A. J. FITZ GERALD.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, lines 59 and 60, for the misspelled word "furname" read "furnace"; line 67, for "commedcial" read "commercial"; and lines 97 and 98, for "rasistors" read "resistors"; page 2, lines 63 and 64, strike out the word "carborundum"; page 3, line 97, claim 4, strike out the word "containing"; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 30th day of July, A. D. 1929.

M. J. Moore, (Seal) Acting Commissioner of Patents. 

